1. Field of the Invention
This invention relates to steering column assemblies for motor vehicles.
2. Background Information
Conventional steering columns for motor vehicles comprise a steering shaft with an axially extending upper shaft part adapted at its upper end for connection to a steering wheel, and adapted at its lower end for connection to a second shaft part, a jacket surrounding the upper shaft part along at least part of its length, and a mounting bracket secured to the jacket for connecting the jacket to the body of a vehicle, the jacket including an energy absorbing element which undergoes deformation when an impact load is applied to the upper shaft part sufficient to move the column part relative to the mounting bracket. For exaple, the jacket may include a circumferentially corrugated section which either collapses or expands in the axial direction under impact conditions.
A bearing is normally provided in the lower part of the jacket to allow the shaft to rotate in the jacket and to prevent the shaft from moving radially relative to the jacket. When an impact load is applied to the upper end of the upper shaft part, the shaft part moves axially downwardly and causes the energy absorbing element to elongate or collapse in the axial direction. If the upper shaft part is connected to a second shaft part coaxial with the upper shaft part by means of a telescopic connection, the upper shaft part will retain its radial orientation with respect to the jacket, and will not interfere with the axial deformation of the energy absorbing element.
In some cases however, it is desirable to connect the upper shaft part to a lower shaft part by means of an intermediate shaft part connected to the other parts by flexible joints, e.g., a universal joint, so that the upper and lower shaft parts can be disposed along different axis. In such an arrangement, if the lower shaft part were to remain stationary when an impact load was applied to the upper shaft part, the intermediate shaft part would tend to move the lower end of the upper shaft part radially; this radial movement would be resisted by the bearing, and the energy absorbing element of the jacket would be unable to deform until sufficient force had been applied to the column to move the lower parts of the shaft radially.